Documentation: gpio: Move introduction to driver-api

Move gpio/intro.txt to driver-api/gpio/intro.rst and make sure it builds
cleanly as ReST.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/driver-api/gpio/index.rst

@@ -2,6 +2,13 @@
 General Purpose Input/Output (GPIO)
 ===================================
 
+Contents:
+
+.. toctree::
+   :maxdepth: 2
+
+   intro
+
 Core
 ====
 

Documentation/gpio/gpio.txt → Documentation/driver-api/gpio/intro.rst

+============
+Introduction
+============
+
+
 GPIO Interfaces
 ===============
 
@@ -9,9 +14,9 @@ Due to the history of GPIO interfaces in the kernel, there are two different
 ways to obtain and use GPIOs:
 
   - The descriptor-based interface is the preferred way to manipulate GPIOs,
-and is described by all the files in this directory excepted gpio-legacy.txt.
+    and is described by all the files in this directory excepted gpio-legacy.txt.
   - The legacy integer-based interface which is considered deprecated (but still
-usable for compatibility reasons) is documented in gpio-legacy.txt.
+    usable for compatibility reasons) is documented in gpio-legacy.txt.
 
 The remainder of this document applies to the new descriptor-based interface.
 gpio-legacy.txt contains the same information applied to the legacy

Documentation/gpio/00-INDEX

 00-INDEX
 	- This file
-gpio.txt
-	- Introduction to GPIOs and their kernel interfaces
 consumer.txt
 	- How to obtain and use GPIOs in a driver
 driver.txt